The Doctor experiences serious regenerative instability, causing him to
attack Peri and then decide to live as a hermit on the barren moon of
Titan. There he stumbles upon a plot by his old friend, the Time Lord
Azmael, who has kidnapped twin mathematical geniuses named Romulus and
Remus. Azmael's adopted planet, Joconda, has been taken over by the
sluglike Mestor and his Gastropods, forcing the Time Lord to do Mestor's
bidding. But even Azmael is unaware of Mestor's true plan -- to destroy
Joconda's sun, and thereby scatter Gastropod eggs throughout the
galaxy.

Production

Part of the motivation behind casting Colin Baker as the Sixth Doctor
was to create as great a contrast with Peter Davison, the outgoing star
of Doctor Who, as Davison had made with his own predecessor, Tom
Baker. Over the summer of 1983, the primary concern of Doctor Who
producer John Nathan-Turner and script editor Eric Saward -- not to
mention Baker himself -- was the development of the new Doctor. It was
agreed that Baker should adopt many of his own larger-than-life
characteristics, diverging from the more subdued demeanour of Davison's
Doctor.

It was also felt that Baker should emphasise the notion that, although
the Doctor may look human, he is nonetheless an alien, with a different
mindset to mankind. The Sixth Doctor would therefore be unpredictable,
argumentative and boisterous, sometimes offering a worldview very much
at odds with his companion's; he would solve problems with dizzying
leaps of logic in the manner of Sherlock Holmes. Baker wanted to make
viewers initially suspicious of his Doctor, but gradually earn their
trust over the course of his tenure. Nathan-Turner aspired to craft a
character similar to the aloof but ultimately reliable Mr Darcy in Jane
Austen's 1813 novel Pride And Prejudice. It was also thought that
the new Doctor should boast very florid dialogue, incorporating both a
plethora of quotations -- both real and fictional -- and a penchant for
obscure vernacular. (Baker hoped that the latter trait would encourage
children to look up the words for themselves in a dictionary, thereby
expanding their own vocabularies.)

Colin Baker wanted to make viewers initially suspicious of
his Doctor, but gradually earn their trust

It was suggested that these defining mannerisms of the Sixth Doctor
should be particularly accentuated in his debut serial, with his
regeneration provoking manic and violent mood swings. Again, this was
meant to provide a contrast with the Fifth Doctor, whose own
introductory story -- Season Nineteen's Castrovalva -- saw him amnesiac, placid and
vulnerable. However, it was agreed that this would be a challenging
depiction to write, especially since Nathan-Turner and Saward had
decided on the unusual move of giving Baker a full serial of his own at
the end of Season Twenty-One, before the break in transmission. The
portrayal of the Sixth Doctor in this adventure, then, would be the
abiding impression in viewers' minds for nine months.

To this end, Nathan-Turner suggested recruiting veteran writer Anthony
Steven, with whom he had worked on All Creatures Great And Small.
Saward agreed to discuss the matter with Steven, although he and
Nathan-Turner had very different impressions of the kind of script that
Steven should write. Nathan-Turner wanted a straightforward adventure
pitting the Doctor against a strong villain, while Saward felt that the
new Doctor's personality would be better showcased in a more unusual
storyline. This was just one of an increasing number of points of
disagreement between the producer and his script editor, amongst them
Saward's unhappiness with Baker's casting in the first place.

Originally a reporter, Steven had been writing for television since the
Fifties. Much of his early work had concentrated on adaptations of
classic novels such as The Three Musketeers and The Man In The
Iron Mask, but Steven had also contributed many original scripts,
including episodes of The Prime Of Miss Jean Brodie and Dr
Finlay's Casebook, in addition to All Creatures Great And
Small. Steven was interested in trying his hand at Doctor
Who, and on July 19th, submitted a storyline entitled “A
Stitch In Time”.

Nathan-Turner and Saward decided to proceed forward with the development
of Steven's serial, and on August 2nd he was commissioned for the script
to episode one; the title had now been amended to “A Switch In
Time”. The remaining installments were contracted on August 24th,
by which time the title had changed again, to The Twin Dilemma.
The character of Azmael was inserted into the story at the prompting of
unofficial fan adviser Ian Levine, who had suggested that the Doctor
should meet his old mentor, referred to in The
Time Monster and State Of Decay.
Unfortunately, Steven misunderstood the nature of the Doctor's
relationship with the character, and made Azmael a tutor at the
Prydonian Academy instead.

Anthony Steven's slow progress was apparently because his
typewriter had “literally exploded”

During the autumn, Steven's progress on The Twin Dilemma slowed
to a crawl. To the mystification of the production team, he began
explaining away his problems with increasingly bizarre excuses -- most
famously, a claim that his typewriter had “literally
exploded”! To make matters worse, The Twin Dilemma did not
meet the approval of its assigned director, Peter Moffat, who had most
recently helmed the twentieth-anniversary special The Five Doctors. Moffat implored Saward to
intervene, pointing out a number of concerns of both a storytelling and
logistical nature. By now, however, Steven had fallen badly ill, and
could not continue working on the serial. The Twin Dilemma would
be his only contribution to Doctor Who; Steven died in May
1990.

Left with no other choice, Saward took on the task of heavily revising
The Twin Dilemma himself. He restructured the climax of the
adventure, shifting it from space back to Joconda and beefing up
Mestor's role. He also excised the suggestion that Mestor was in fact
possessed by an extraterrestrial intelligence called Aslan. The
Chamberlain was originally female, while Commander Fabian (apparently an
homage to the Fifties crime drama Fabian Of Scotland Yard) was
male, and merely a general. Azmael, meanwhile, was a reference to the
fallen angel Azazel, while Remus and Romulus Sylvest were named after
the legendary founders of Rome.

While the scripts for The Twin Dilemma were slowly hammered into
shape, other elements of the new era of Doctor Who were falling
into place. Having been contracted for the final five episodes of Season
Twenty-One on September 30th, Baker's services for Season Twenty-Two
were secured on October 4th. This contract also included an option for
three additional years: Nathan-Turner was keen to avoid the brevity of
Davison's tenure, while Baker -- long an enthusiastic fan of Doctor
Who -- was in fact eager to eclipse Tom Baker's record seven seasons
on the show.

Colin Baker preferred a black velvet outfit, but John
Nathan-Turner vetoed this as too similar to the Master

The new star and his producer were less like-minded on the topic of the
Sixth Doctor's costume. Baker preferred a black velvet outfit, but
Nathan-Turner vetoed this on the grounds that it was too similar to the
Master's usual dress. Instead, the producer wanted something totally
tasteless to replace Davison's understated cricketing garb, and costume
designer Pat Godfrey had to go back to the drawing board several times
before finally devising something which Nathan-Turner felt was
sufficiently garish. Godfrey was instructed to omit the colour blue from
his pallet (since this would interfere with special effects shots using
the Colour Separation Overlay technique), and was asked to retain the
question-mark collars that Nathan-Turner had introduced in 1980. For his
part, Baker decided to add a cat badge to the ensemble, which he would
often swap out; this was inspired by “The Cat That Walked By
Himself”, from Rudyard Kipling's 1902 anthology Just So
Stories. Baker was otherwise reluctant to embrace Nathan-Turner's
chosen design; indeed, years later, the producer admitted that the
costume had been a mistake, and worked against the show.

Disaster nearly struck The Twin Dilemma in December, when a
strike by the BBC's scenery shifters crippled Davison's farewell
adventure, The Caves Of Androzani. One of
the serial's two studio sessions was lost as a result, leaving
Nathan-Turner no choice but to reallocate the first studio block for
The Twin Dilemma, from January 10th to 12th, 1984, to the Fifth
Doctor's swansong. One year earlier, a similar set of circumstances had
caused the loss of the Season Twenty finale (eventually made as Resurrection Of The Daleks for Season
Twenty-One). Fortunately, this time, Nathan-Turner was able to secure a
new studio session for The Twin Dilemma, successfully arguing to
his superiors about the importance of the new Doctor's introductory
adventure.

Despite the postponement of production on his debut story, Colin Baker
and his outlandish new costume were still unveiled to the press on
January 10th. Despite Baker's ebullience, this was in fact a tragic time
for his family: some weeks earlier, his two-month-old son Jack had
fallen victim to Sudden Infant Death Syndrome (SIDS). Baker would go on
to make the cause of SIDS research and awareness an important part of
his life's work.

Peter Moffatt believed he had located twin girls who would
be suitable to play the Sylvests, but John Nathan-Turner was opposed to
the change of gender

As production neared on The Twin Dilemma -- now designated Serial
6S -- Moffatt found himself bedeviled with the difficulty of casting
identical twin teenaged boys as Remus and Romulus Sylvest. At one point,
Moffatt believed that he had located twin girls who would be suitable,
but Nathan-Turner was opposed to the change of gender. At the last
minute, Moffatt was approached by an agent representing Andrew and Gavin
Conrad (the latter going by the stage name “Paul” to avoid
confusion with another actor named Gavin Conrad). Moffatt was
unimpressed by the boys' acting ability and lack of experience, but
reluctantly hired them all the same.

Due to the delay incurred by the industrial action, recording for The
Twin Dilemma began with what was originally to have been its second
three-day block, from January 24th to 26th in BBC Television Centre
Studio 8. The first two days dealt with scenes in the TARDIS and in the
Titan Three safe house; also recorded on the 24th was material on
“Edgeworth's” spacecraft (during which Colin Baker provided
the voice of Jaconda Control), with the ducting set in use on the 25th.
The last day of the block tackled more scenes on the spaceship, as well
as those in the Sylvest twins' playroom and the ops room.

Two days of location filming were allocated to The Twin Dilemma.
On February 7th, Springwell Quarry in Rickmansworth, Hertfordshire posed
as the surface of Titan Three, while the next day, exterior scenes on
Joconda were shot at Gerrards Cross Gravel Pits in Wapseys Wood,
Buckinghamshire. By now, Baker and Nicola Bryant were beginning to warm
up to each other after a frosty start to their relationship: Bryant had
been nervous about suddenly becoming the senior member of the regular
cast, and Baker had mistaken this for standoffishness on her part.

The rescheduled studio session for Serial 6S took place from February
14th to 16th in TC3. Taping took place on the sets for Mestor's throne
room and various corridors on all three days, while Azmael's lab was
also needed on the 14th and 15th. The TARDIS console room was once again
required for the final day of recording, which drew the production of
Season Twenty-One to a close.

In Sid Sutton's new title sequence, two images of Colin
Baker were used to make the Doctor appear to smile

There was still work to be done before the new Doctor could make his
televised debut, however. Most notably, a revised version of the credit
sequence was required and this was assembled by Sid Sutton, who had
introduced the “starfield” sequence for Tom Baker's final
season in 1980. This time, he worked with Terry Handley to add a rainbow
effect to the graphics, and used two images of Baker to make the new
Doctor appear to smile. Sutton also revised the neon logo, changing the
colour and slightly distorting its flat shape.

Heralded by this amended title sequence, viewers enjoyed their first
full Sixth Doctor episode on March 22nd. Eight days later, on March
30th, the final installment of The Twin Dilemma brought Doctor
Who's twenty-first season to a close.